This invention relates to plain-end pipe couplings and a method and apparatus for manufacturing same and more specifically, to plain-end pipe couplings made of fibrous glass reinforced plastic wrapped or applied on a collapsible mandrel utilizing a polyurethane mold collar and, to a method and apparatus for manufacturing same.
Many underground water systems have historically been made of vitrous clay pipe coupled together at abutting ends by a bell and a spigot. Of late attempts have been made to utilize "plain-end" pipes, or pipes that have a uniform diameter throughout their whole length. Plain-end pipes have been found to be more efficient to produce but are problematic in respect to providing an adequate watertight seal at their junction.
Water leakage can occur axially along an outer cylindrical surface of the pipe as a result of a coupling that doesn't seal the pipe thouroughly. This usually occurs because either because of a size or shape difference the coupling lacks adequate sealing ability around the coupling mating surface of the pipe or because of a non-uniformity in the diameter of the pipe at the point of sealing. Leakage can also occur because of a shear strain occuring in the coupling at the point of the junction between the pipes themselves.
In many prior art couplings, the coupling is unable to provide a seal along the total cylindrical surface of the pipe or, if able to provide an adequate seal as such, the couplings are normally pliable or nonrigid in nature and do not have the required structural strength or integrity to resist forces acting in a shear direction between the two pipe ends, thereby allowing the pipe to separate and/or the pipes and the coupling to separate and therefore produce a water leak.
Another drawback in the prior art is associated with the complicated design of many of the conventional couplings, some of which couplings have had an elastomeric binding with fibers fabricated therearound. Other conventional couplings have had an inner section situated between two outer end sections with each section being laminated with different materials.